CSAT 2021

Q. When a certain number is multiplied by 7, the product entirely comprises ones only (1111…). What is the smallest such number?

(a) 15713
(b) 15723
(c) 15783
(d) 15873
Correct Answer: (d) 15873

Question from UPSC Prelims 2021 CSAT Paper

Explanation : 

Best Method- Check All option
15873 × 7 = 111111

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